C4 Transmission Doesnt Shift to Third!!

Discussion in 'Transmissions' started by mustangman66, Aug 18, 2011.

  1. mustangman66

    mustangman66 New Member

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    I have a 66 c4 green dot that refuses to engage third gear. Ive replaced the modulator, oil and adjusted everything but i still have no progress. Its rather frustrating and id like to know if anyone had any idea what this could be. Thanks so much for your help.
     
    mustangman66, Aug 18, 2011
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  2. mustangman66

    mustangman66 New Member

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    So it could be the gasket between the carb spacer and the intake log?
     
    mustangman66, Aug 18, 2011
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  3. 71gold

    71gold Frank Cooper Supporting Member

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    check for a split in the modulator vac. line.
    i also had one that the vac. line had become soft and was collasping shut under vac.

    ...:tiphat:...
     
    71gold, Aug 18, 2011
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  4. mustangman66

    mustangman66 New Member

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    Actually the hose connecting the steel line to the modulator is a soft one that seems easy to push in. Is it supposed to be a stiffer, thicker hose?
     
    mustangman66, Aug 18, 2011
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  5. Jsarnold

    Jsarnold Senior Member

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    Jsarnold, Aug 18, 2011
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  6. mustangman66

    mustangman66 New Member

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    That is precisely what it looks like. So could it be the deteriorating line connecting intake manifold to the steel line? It is rather burnt up but im getting a pretty good vacuum reading at the manifold. Somewhere in the 19's and 20's
     
    mustangman66, Aug 18, 2011
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  7. mustangman66

    mustangman66 New Member

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    Is there a way i could check if the transmission would shift to third otherwise?
     
    mustangman66, Aug 18, 2011
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  8. whitey68

    whitey68 Member

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    check your kick down, make sure it returns back up when you push it down
     
    whitey68, Aug 19, 2011
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  9. mustangman66

    mustangman66 New Member

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    Checked the kick down and it definitely returns.
     
    mustangman66, Aug 19, 2011
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  10. PaulS

    PaulS Member extrordiare

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    Check the vacuum at the modulator - it has to be 10 or above.
    Could be a bad hose at either end of the metal line or a cracked line to the modulator.
    If you have reverse then it might be a stck 2-3 shift valve if the vacuum is above 10 at the modulator.
    It would help to know what speeds the transmission shifts from 1 to 2 also.
    Paul
     
    PaulS, Aug 30, 2011
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  11. KauaiHi

    KauaiHi Member

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    where is the vaccuum mod hose?

    where is the vaccuum mod hose?
     
    KauaiHi, Oct 27, 2011
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  12. PaulS

    PaulS Member extrordiare

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    It connects to the modulator located at the passenger (right) rear corner of the main case - just above the trans pan. Test it there with the engine idling in park.
    It should connect to the manifold vacuum either at the rear of the carb mount on the manifold or the vacuum tree on the firewall.
     
    PaulS, Oct 28, 2011
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